Inventions described herein relate to improved apparatus and methods that can be used in assembling a printed circuit board or printed wiring board, particularly in wave soldering systems.
Wave soldering systems utilize wave nozzles of various designs and configurations that incorporate pumps to produce a wave of molten solder through which printed circuit boards are conveyed for solder application. Ideally, wave nozzles should be designed and constructed to deliver a smooth, non-turbulent solder wave to a solder application site. Many wave nozzles, however, do not accomplish this objective and produce solder waves that are not sufficiently smooth and which are turbulent. Further, many wave nozzle configurations comprise numerous components that must be periodically disassembled during wave soldering for maintenance and cleaning and, more particularly, for removal of dross.
Dross comprises metal oxides which form at the interface between air and the surface of molten solder. As a solder wave moves through a wave nozzle, the surface of the solder wave is often turbulent from the action of nozzle components generating and circulating the solder wave from a molten solder pot or reservoir to the site of solder application through which printed circuit boards are conveyed. Such turbulence exposes metal alloys at the surface of the solder wave to air causing the metal alloys to interact with air and oxidize to form metal oxides. Dross is an accumulation of such metal oxides typically formed on the surface of molten solder held in reservoirs and on wave nozzle components exposed to solder wave turbulence. Dross accumulation must be removed from nozzle components to maintain the performance of the wave nozzle. Therefore, wave nozzles are periodically disassembled during operation for maintenance and dedrossing.
Existing methods for reducing the formation of dross in wave nozzles include application of oil to the surface of the solder wave, the incorporation of a dross reduction tray, as disclosed in U.S. Pat. No. 4,802,617, assigned to the assignee of the present invention, and maintenance of a particular level of solder in a solder receiving tray that minimizes the free fall of molten solder on return of molten solder to a reservoir, as disclosed in U.S. Pat. No. 4,886,201, assigned to the assignee of the present invention.
Although existing wave nozzle construction and wave soldering techniques reduce dross formation, they do not reduce dross formation sufficiently to significantly reduce production downtime and operational costs associated with disassembling and dedrossing wave nozzle components. Measures to reduce the turbulence of a solder wave would reduce the susceptibility of a solder wave to surface oxidation and, therefore, would reduce dross formation on nozzle components. In addition, existing nozzles cause splashing of molten solder typically at a load site when a wave nozzle begins operation. Tiny droplets of molten solder can splash from a solder wave and disperse outside a wave nozzle, producing hazardous bum conditions. Measures to reduce splashing of molten solder in wave soldering would reduce such a hazard.
Additionally, a wing device may be used as part of the nozzle. The nozzle may include a chimney, or tunnel, which typically directs the flow of a solder wave. The solder may then flow over various plates to provide a reservoir of liquid for a printed circuit board (PCB) to contact. For example, in a wave solder machine, a PCB may travel from a front plate toward a wing device while its leads are being soldered. Every time a different PCB passes through a wave solder machine the wing device may need to be adjusted.
Previous wing devices required the machine to be stopped, and the solder pot, or reservoir of solder, to be lowered so that the wing height could be adjusted to accommodate a different PCB in a new batch. This procedure is time consuming, difficult and dangerous due to the high temperature of the solder. A typical solder pot may hold 2,000 pounds (900 kg) of solder at temperatures in excess of 500xc2x0 F. (260xc2x0 C.). The operator has to stop the wave solder machine and lower the solder pot which causes expensive production line downtime. These long setups lead not only to increased machine downtime, but also to more setup PCB and solder scrap. This discontinuous setup process may also make it difficult to obtain a high quality solder joint in a reasonable amount of time. If the first machine setup is incorrect, the machine must be stopped again, and the setup process steps repeated (more downtime) until a quality solder joint is produced or until the operator accepts the marginal quality and runs the boards.
Optimal accuracy of the device is obtained by designing a system that has a level reservoir of solder. Previous wave solder machines have used unstable wing devices that are prone to bowing and twisting under the extreme thermal stress, resulting in a non-level wave of solder. Without a level plane of solder, inconsistent solder joints are formed across the length of each printed circuit board resulting in increased PCB rejections. Bowing and twisting of the wing element may also cause solder leakage which, in turn, leads to excessive dross formation.
Solder leakage along the wing device is also a problem because it causes excessive turbulence, and therefore, excessive oxidation of the solder, which produces (dross) waste. The removal of this dross then leads to machine downtime and wasted maintenance resources. Previous wing devices, or solder nozzle systems, also suffered from leakage due to warpage of the wing device.
Previous wave soldering systems have also included mounted members for handling substrates after the substrates pass over the nozzle. However, the mounted members have not been easily adjustable to accommodate differences in the amount of solder applied to different substrates as well as other processing differences.
A wave soldering system of this invention includes a wave nozzle having a chimney that defines a passage through which solder can be delivered. The chimney has a source end that can be coupled with a source of solder, such as a solder pot, and an exit from which the solder can be ejected onto a substrate. The wave nozzle further includes adjustable components that enhance operation efficiency. In accordance with various aspects of the invention, the system can include a pivotable wing element and/or a pivotable gate for directing solder flow out of the nozzle as well as an adjustable mounting device for handling substrates after they pass over the wave nozzle. All of these components can be mounted on a solder pot.
In accordance with one aspect of the invention, a pivotable wing element is attached to a hinge at an end proximate to the exit of the nozzle, and an adjustable member is provided to rotate the wing about the hinge to thereby raise and lower a solder wave when the nozzle is operating. In one embodiment, the adjustable member includes a rotatable shaft to which a protruding member is fixed.
In accordance with another aspect of the invention, a pivotable gate can be mounted to swing toward and away from a front plate over which the solder wave flows. The gate can be pivoted to accommodate more or less solder flow between the gate and the front plate. The gate can also include a perforated baffle angled to reduce turbulence in a solder wave. The mounting device can include a mounted member, such as a hot air knife, positioned to act on a substrate after it passes over the nozzle. In one embodiment, the mounting device is mounted on the solder pot and the mounted member is rotatable toward and away from the nozzle.
Many advantages are offered by the various aspects of this invention.
In accordance with one aspect of the invention, the wing device of a wave nozzle is designed for quick and easy adjustment. Easy adjustment of the wing element decreases machine downtime due to quicker setups and maintenance of the machine. Designs of the wing device, described herein, also substantially eliminate bowing and twisting of the wing device during nozzle operation. Additionally, solder leaks, which cause increased turbulence, oxidation of solder and formation of dross, can be eliminated or greatly reduced by embodiments of the wing device described herein. Reducing leaks and dross formation substantially reduces the maintenance required to clean off dross and reduces wasted solder. Further still, the wing device can reduce wave solder machine setup time and down time and improve PCB quality by ensuring consistent quality solder joints.
In accordance with another aspect of the invention, a wave nozzle with a front gate can be constructed to eliminate the hazards associated with splashing molten solder and reduce dross formation on wave nozzle components to reduce production downtime and operational costs associated with wave soldering.
With each different PCB that passes across the nozzle, there are different components and lead lengths, and therefore different amounts of solder being applied to the PCB. Every time a new batch of PCB""s is passed through the machine, the mounted member may need to be adjusted and therefore, a quick adjustment mechanism is desired. Use of a mounting device of this invention can provide such a quick and easy adjustment means. In particular, the mounting devices described herein can ensure quick and easy access to the structure upon which it is mounted (e.g., a solder pot) due to the easy movement of the mounting device from a process position to the maintenance position. Setup and down times on the machine or solder pot are thereby reduced. Additionally, easy and real-time four-way adjustability of the mounting device can be offered while the machine or solder pot is running in the process position, thereby providing quicker setup times, less downtime and higher quality PCB""s.